Orthopaedic implants are typically mechanically hammered into position either through use of a mallet or a repetitive automated hammer. In both cases, force is applied by a mallet/hammer and through an impactor to an implant. Bone preparation typically uses a broach which may be hammered into the bone—the force being applied through a broach handle. On some occasions a trial implant may be hammered into the bone—the force being applied through an impactor or handle.
While a certain force is required to drive the implant into position, the force must not be so high that it causes fracturing of the bone.
Particularly, one complication associated with the implant process is the formation of a longitudinal split in the bone known as a periprosthetic fracture (PPF) which results from hoop stress in the bone (created by insertion of the implant or broach or trial implant) exceeding the strength of bone. PPFs are a significant cause of intraoperative morbidity and one of the most common causes of early post-operative failure of prosthetic components.
PPF is a particularly serious complication of Total Hip Arthroplasty (THA) and occur around both acetabular and the femoral components. The incidence of PPF is significantly higher in revision procedures than it is in primary procedures. The incidence of PPF is also significantly higher in cementless or press fit procedures than in cemented procedures. The incidence is also higher in the elderly and in those with fragile bone.
PPF can be divided into three time-based categories; Intra-operative fractures detected at the time of surgery, fractures in the early post operative period, and postoperative fractures occurring late after procedure.
The incidence of PPFs detected at the time of surgery have been reported in primary cementless femoral implantations to be as high as 5.4%. In revision femora, the incidence of femoral fracture detected at the time of surgery is much higher with cementless revision procedures being reported as high as 21%. The prevalence of these fractures has increased since the introduction of cementless press fit acetabular components. However, there still is surprisingly little in the orthopaedic literature regarding acetabular PPF at the time of surgery.
Further, the problem of intra-operative PPF in both the femur and acetabulum might be more prevalent than reported. It is argued that fractures occurring in the early post operative period may well be undiagnosed intra-operative PPFs. Whatever the incidence of intra-operative PPF the severity of the problem is highlighted by the poor outcomes reported.
Currently, there is no useful mechanism by which a surgeon can determine the risk of fracture both during and after an operative procedure.
The present invention aims to address the abovementioned shortcomings and provide a safety system to minimise the risk of fracture during and after implant procedures.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.